Semiconductor optical component and manufacturing method therefor

ABSTRACT

A manufacturing method for a semiconductor optical component in which ridge-shaped semiconductor light amplifier sections and ridge-shaped semiconductor waveguides connected thereto are integrated on the same substrate includes the steps of forming the ridge-shaped semiconductor light amplifier sections having a path width narrower than that of the ridge-shaped semiconductor waveguide at the appropriate positions on the substrate on which the ridge-shaped semiconductor light amplifier sections are to be formed; and forming the ridge-shaped semiconductor waveguide at the remaining positions other than the appropriate positions so as to connect to the ridge-shaped semiconductor light amplifier sections. The semiconductor optical component manufactured by this method provides high current density because the confining of the current injected to the light amplifier is strengthened. Therefore, it is useful as an optical component which can perform light amplification efficiently even if a small current is injected.

TECHNICAL FIELD

The present invention relates to a semiconductor optical component, inwhich ridge-shaped semiconductor light amplifier sections andridge-shaped semiconductor waveguides are integrated on the samesubstrate in a connected state, and a manufacturing method therefor and,more particularly, a semiconductor optical component, in which electriccurrent of a high current density can be injected to the semiconductorlight amplifier section because the current confining effect is largewhen the semiconductor light amplifier section is operated, andtherefore light amplification can be effected efficiently even if asmall current is injected, and a manufacturing method therefor.

BACKGROUND ART

A manufacturing method for a semiconductor light switch having asemiconductor light amplifier section and a semiconductor waveguideintegrated on the same substrate has been disclosed in IEEE PhotonicsTechnology Letters, vol. 2, pp. 214-215, March 1990.

With this method, thin layers of a predetermined semiconductor aresuccessively laminated on the entire surface of a semiconductorsubstrate so as to correspond to the layer structure of a lightamplifier section to be formed in order to form a lower cladding layer,a core layer, and an upper cladding layer. Then, the laminated body ofthe semiconductor thin layers in the area other than the area in which alight amplifier section is to be formed is etched and removed to exposethe surface of the substrate, and thereafter thin layers of apredetermined semiconductor are successively laminated on the exposedsurface of the substrate so as to correspond to the layer structure of awaveguide to be formed in order to form a lower cladding layer, a corelayer, and an upper layer.

Subsequently, a switching section is formed by diffusing, for example,Zn in a predetermined area of the waveguide, the entire construction isetched to form a ridge-shaped waveguide having the same width, a desiredpattern, and a desired height in the upper cladding layers of thelaminated bodies corresponding to the light amplifier section and thewaveguide, respective electrodes are mounted on the switching sectionand the light amplifier section, and a common electrode is mounted onthe back surface of the substrate.

In this semiconductor light switch, the waveguide and the lightamplifier section formed in a ridge shape have an equal path width.Switching operation is performed by injecting electric current to theswitching section of the waveguide, whereas light amplification isperformed by injecting electric current to the light amplifier section.

Japanese Patent Laid-Open No. 2-199430 discloses a semiconductor lightswitch which has waveguides of an equal width crossing in an X form, abypass waveguide formed between the input port and the output port ofrespective waveguides and having a width equal to that of the aforesaidwaveguide, and a light amplifier section formed on the bypass waveguide.The sectional construction of the waveguide, light amplifier section,and switching section of this semiconductor light switch is similar tothat disclosed in IEEE Photonics Technology Letters.

In any of the light switches of two kinds described above, theconfinement of light transmitted to the core layer at the waveguide andlight amplifier section is effected by the equal-width ridges formed inthe respective upper cladding layers.

For the light switches of this construction, the path width of the corelayer through which light is substantially transmitted is equal for thewaveguide and the light amplifier section. For this reason, the effectof confining the injected current is small when electric current isinjected to the light amplifier section; therefore, it is difficult toincrease the current density of the injected current. As a result, it isdifficult to achieve highly efficient light amplification.

DISCLOSURE OF THE INVENTION

An object of the present invention is to solve the above problem withthe light switch in which waveguides and light amplifier sections areintegrated on the same substrate, and to provide a semiconductor opticalcomponent in which the confining state of the current injected to thelight amplifier section is strengthened, thereby light amplificationbeing performed with high efficiency, and a manufacturing methodtherefor.

The present invention provides a semiconductor optical componentcomprising a ridge-shaped semiconductor light amplifier section and aridge-shaped semiconductor waveguide connected thereto, which are formedon the same substrate, wherein the path width of the ridge-shapedsemiconductor light amplifier section is narrower than that of theridge-shaped semiconductor waveguide. Preferably, a semiconductoroptical component is provided in which the ridge height of theridge-shaped semiconductor light amplifier section is greater than thatof the ridge-shaped semiconductor waveguide.

Further, the present invention provides a manufacturing method for asemiconductor optical component in which ridge-shaped semiconductorlight amplifier sections and ridge-shaped semiconductor waveguidesconnected thereto are integrated on the same substrate, comprising thesteps of forming the ridge-shaped semiconductor light amplifier sectionshaving a path width narrower than that of the ridge-shaped semiconductorwaveguides at the appropriate positions on the substrate on which theridge-shaped semiconductor light amplifier sections are to be formed;and forming the ridge-shaped semiconductor waveguide at the remainingpositions other than the appropriate positions so as to connect to theridge-shaped semiconductor light amplifier sections.

Preferably, there is provided a manufacturing method for a semiconductoroptical component in which the ridge-shaped semiconductor lightamplifier section is formed in such a manner that the ridge heightthereof is greater than that of the ridge-shaped semiconductorwaveguide.

In the semiconductor optical component manufactured by the method of thepresent invention, since the path width of the light amplifier sectionis narrower than that of the waveguide, the confining of the injectedcurrent is increased at the light amplifier section, thereby the currentdensity being increased. As a result, light can be amplified at highefficiency.

Also, the coupling efficiency of light can be increased because theridge height of the light amplifier section is greater than that of thewaveguide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a total reflection type light switchmanufactured by the method of the present invention.

FIG. 2 is a partial sectional view showing the waveguide layer, activelayer, waveguide layer, cladding layer, and surface layer laminated on asubstrate.

FIG. 3 is a partial sectional view showing a condition in which alaminated body a₁ (a₂) of a section to be operated as a light amplifiersection is formed.

FIG. 4 is a partial sectional view showing a condition in which awaveguide layer, upper cladding layer, and surface layer of a waveguideare formed on the substrate surface.

FIG. 5 is a sectional view taken along the line V--V of FIG. 1.

FIG. 6 is a sectional view taken along the line VI--VI of FIG. 1.

FIG. 7 is a partial sectional view showing a condition in which awaveguide layer, first upper cladding layer, etch stop layer, secondupper cladding layer, and surface layer of a waveguide are formedsurrounding a light amplifier section when an optical component having alight amplifier section of a high ridge shape is manufactured.

FIG. 8 is a partial sectional view showing a condition in which thelight amplifier section in the construction shown in FIG. 7 is etchedwith an etchant including sulfuric acid.

FIG. 9 is a partial sectional view showing a condition in which thewaveguide in the construction shown in FIG. 7 is etched with an etchantincluding sulfuric acid.

FIG. 10 is a partial sectional view showing a condition in which theconstruction shown in FIG. 8 is etched with an etchant includinghydrochloric acid.

FIG. 11 is a partial sectional view showing a condition in which theconstruction shown in FIG. 9 is etched with an etchant includinghydrochloric acid.

FIG. 12 is a partial sectional view showing the sectional constructionof the light amplifier section.

FIG. 13 is a partial sectional view showing the sectional constructionof the switching section.

FIG. 14 is a schematic plan view of a directional coupler type lightswitch manufactured by the method of the present invention.

FIG. 15 is a sectional view taken along the line XV--XV of FIG. 14.

FIG. 16 is a schematic plan view of a 1×2 optical coupler manufacturedby the method of the present invention.

FIG. 17 is a sectional view taken along the line XVII--XVII of FIG. 16.

FIG. 18 is a graph showing the relationship between path width andamplification factor.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows an example of total reflection type light switchmanufactured by the method of the present invention. In the figure, twowaveguides 2 and 3 crossing each other are formed on a semiconductorsubstrate 1 by laminating thin layers of a predetermined semiconductor.At the cross section, an electrode 4 for injecting electric current ismounted to form a switching section S.

A waveguide 5 formed by laminating thin layers of a predeterminedsemiconductor is connected to a port 2b of the waveguide 2 at a port 5a,whereas a waveguide 6 formed by laminating thin layers of apredetermined semiconductor is connected to a port 3b of the waveguide 3at a port 6a.

At the intermediate portion of the waveguide 5 extending from the port5a to a port 5b, a light amplifier section A₁ is formed which has a pathwidth smaller than that of the waveguide 5 and is provided with anelectrode 23. Likewise, at the intermediate portion of the waveguide 6extending from the port 6a to a port 6b, a light amplifier section A₂ isformed which has a path width smaller than that of the waveguide 6 andis provided with an electrode 23.

This light switch is manufactured by the method described below. Thismethod will be described with reference to the drawings.

As shown in FIG. 2, for example, a waveguide layer 12 formed of n-typeInGaAsP semiconductor, an active layer 13 formed of undoped InGaAsPsemiconductor, and a waveguide layer 14 formed of p-doped InGaAsPsemiconductor are successively laminated on the surface of a substrate11 formed of, e.g., n-type InP semiconductor by using a film formingtechnique such as the MOCVD method. Further, for example, an uppercladding layer 15 formed of p-doped InP semiconductor and a surfacelayer 16 formed of p-doped InGaAs semiconductor are successivelylaminated on the waveguide layer 14. Here, the waveguide layer 12constitutes a lower cladding layer, and the active layer 13 and thewaveguide layer 14 constitute a core layer.

Of the slab-shaped laminated body thus formed on the substrate 11, onthe surface layer 16 in the area a₁ (a₂) functioning as a lightamplifier section, an insulating film 17 such as SiO₂ film is formed.This film is used as a mask, and the portion of the laminated bodyexcluding the area a₁ (a₂) is etched and removed so as to expose thesurface 11a of the substrate 11 as shown in FIG. 3.

Then, a waveguide layer 18 formed of, e.g. undoped InGaAsP semiconductoris formed on the exposed surface 11a of the substrate only, as shown inFIG. 4, for example, by the MOCVD method so that its thickness reachesthe middle of the upper cladding layer 15. Further, a cladding layer 19formed of, e.g. undoped InP semiconductor and a surface layer 20 formedof, e.g. undoped InGaAs semiconductor are successively formed over thewaveguide layer 18 only.

Thus, a waveguide section is formed by a laminated body b consisting ofthe waveguide layer 18, the cladding layer 19, and the surface layer 20,so that the laminated body a₁ (a₂) formed to constitute a lightamplifier section A₁ (A₂) is surrounded by the laminated body b formedto constitute a waveguide.

Then, the insulating film 17 on the laminated body a₁ (a₂) is removed,and an elevated stepped or ridge-shaped waveguide of a planar patternincluding the switching section S and the light amplifier section A₁(A₂) as shown in FIG. 1 is formed. Thereafter, the entire surface of thelaminated bodies a₁ (a₂) and b are covered again with an insulating film21 such as SiO₂.

Next, as shown in FIG. 5, which is a sectional view taken along the lineV--V of FIG. 1, a lower common electrode 22 is mounted by depositing amaterial such as AuGeNi/Au on the back surface of the substrate 11.Further, a part of the insulating film 21 on the laminated bodycorresponding to the light amplifier section a₁ (a₂) is removed to forma window 21a. From here, a material such as Ti/Pt/Au is deposited on thesurface layer 16 to mount an upper electrode 23, 23 for the lightamplification, thereby the light amplifier section A₁ (A₂) being formed.

As shown in FIG. 6, which is a sectional view taken along the lineVI--VI of FIG. 1, in the switching section S, a part of the insulatingfilm 21 covering the switching section S is removed to form a window21b. Zn diffusion zone 24 is formed by diffusing, e.g., Zn from thiswindow. Then, a material such as Ti/Pt/Au is deposited on the surfacelayer 20 to mount an upper electrode 4 for a switching operation,thereby the switching section S being formed.

For this light switch, for example, if light is introduced through theport 3a without current injection from the electrodes 4, 23, and 23 inFIG. 1, the incident light passes through the waveguide 3, the port 3b,the port 6a, the light amplifier section A₂, and the waveguide 6, andthen goes out through the port 6b. Hereinafter, this state is called theswitch state I.

If light is introduced through the port 3a with current being injectedthrough the electrode 4 but other electrodes 23, 23 being not inoperation, the incident light passes through the waveguide 3, theswitching section S, the waveguide 2, the port 2b, the light amplifiersection A₁, and the waveguide 5 by the action of the switching sectionS, and then goes out through the port 5b. Hereinafter, this state iscalled the switch state II.

In the switch state I, if current is injected through the electrode atthe light amplifier section A₂ with the electrode at the light amplifiersection A₁ being not in operation, the light transmitted from the port3a to the waveguide 6 is amplified at the light amplifier section A₂.

In the switch state II, if current is injected through the electrode atthe light amplifier section A₁ with the electrode at the light amplifiersection A₂ being not in operation, the light transmitted from the port3a to the waveguide 5 by changing the optical path at the switchingsection S is amplified at the light amplifier section A₁.

In either operation, since the path width at the light amplifier sectionA₁ (A₂) is narrower than the path width of the waveguide 5 (6), theconfining of the injected current is not weakened as compared with thecase of equal width, thereby highly efficient light amplification beingachieved.

Next, a manufacturing method for a semiconductor optical component willbe described by using a total reflection type switch as an example. Inthe total reflection type switch, the height of the ridge or elevatedstep at the light amplifier section is greater than that at thewaveguide; therefore, the coupling efficiency of light to the activelayer can be further increased.

First, as shown in FIGS. 2 and 3, a waveguide layer 12 formed of n-typeInGaAsP semiconductor, an active layer 13 formed of undoped InGaAsPsemiconductor, a waveguide layer 14 formed of p-doped InGaAsPsemiconductor, an upper cladding layer 15 formed of p-doped InPsemiconductor, and a surface layer 16 formed of p-doped InGaAssemiconductor are successively laminated on a substrate 11. Thereafter,on the portion of the laminated body thus formed on the substrate 11,including a part of the laminated body functioning as a light amplifiersection, an insulating film 17 such as SiO₂ film is formed. This film isused as a mask, and the entirety of the laminated body excluding theabove-mentioned part is etched and removed so as to expose the surface11a of the substrate 11.

Then, as shown in FIG. 7, a waveguide layer 18' formed of, e.g. undopedInGaAsP semiconductor is formed only on the exposed surface 11a of thesubstrate so that its thickness reaches the height of the waveguidelayer 14. Further, a first upper cladding layer 19'a formed of undopedInP semiconductor, an etch stop layer 25 formed of undoped InGaAsPsemiconductor, a second upper cladding layer 19'b formed of undoped InPsemiconductor, and a surface layer 20' formed of undoped InGaAssemiconductor are successively laminated to form a laminated body b' forconstituting a waveguide.

Next, the insulating film at the portion including the area where thelight amplifier section is formed is temporarily removed to expose thesurface layer 16. Thereafter, as shown by a planar pattern in FIG. 1, apattern of insulating film 17' such as SiO₂ is formed by covering thearea where the light amplifier section A₁ (A₂) is to be formed and thearea where the switching section S and the waveguide 2, 3, 5, and 6 areto be formed. By using this film as a mask, the entire surface layers20' and 16 exposed to the surface are removed by using, for example, anetchant including sulfuric acid. In this process, the pattern of theinsulating film 17' is drawn in such a manner that the pattern pathwidth of the area where the light amplifier section A₁ (A₂) is to beformed is smaller than that where the waveguide 2, 3, 5 and 6 is to beformed.

As the result of etching process, the area where the light amplifiersection A₁ (A₂ ) is to be formed has a sectional construction as shownin FIG. 8, whereas the area where the switching section S and thewaveguide 2, 3, 5, and 6 are to be formed has a sectional constructionas shown in FIG. 9.

Then, by performing etching using, e.g., an etchant includinghydrochloric acid in place of a sulfuric acid etchant, the portion ofupper cladding layer 15 exposed in the area where the light amplifiersection A₁ (A₂) is to be formed is removed as shown in FIG. 10. At thesame time, as shown in FIG. 11, the second upper cladding layer 19'bexposed in the area where the waveguide and the switching section to beformed is removed to form a light amplifier section having a path widthW₁ and a waveguide having a path width W₂ (W₂ >W₁). In this process,etching does not proceed beyond the etch stop layer 25 at the waveguideand the switching section S by the action of etch stop layer 25.

After the insulating film 17' of the planar pattern shown in FIG. 1 isremoved temporarily, the entire surface is covered again to form aninsulating film 21 such as SiO₂ film. On the back surface of thesubstrate 11, a lower common electrode 22 is mounted in the same way asshown in FIG. 5. In the area where the light amplifier section A₁ (A₂)is to be formed, a window 21a is formed in the insulating film 21, andan upper electrode 23 for light amplification is mounted as shown inFIG. 12. At the switching section S, a window 21b is formed in theinsulating film 21, from which, e.g., Zn is diffused to form a Zndiffusion area 24 as shown in FIG. 13. Thereafter, an upper electrode 4for a switching operation is mounted.

Thus, the light amplifier section A₁ (A₂), the waveguides 2, 3, 5, and6, and the switching section S are formed, either of which is of a ridgeshape. The path width W₁ of the light amplifier section A₁ (A₂) isnarrower than the path width W₂ of the waveguide 2, 3, 5, and 6connecting to the light amplifier section A₁ (A₂). Although the pathheight of all of the light amplifier section A₁ (A₂), the surfaces ofthe waveguides 2, 3, 5, and 6, and the switching section S constitutethe same plane, at the light amplifier section A₁ (A₂), the base is dugfrom the surface of the surrounding etch stop layer 25 to the waveguidelayer 14. Therefore, the ridge height (h₁) of the light amplifiersection A₁ (A₂) from the waveguide layer 14 to the surface of thesurface layer 16 is greater than the ridge height (h₂) of the waveguide2, 3, 5, and 6 from the etch stop layer 25 to the surface of the surfacelayer 20' of the waveguide 2, 3, 5, and 6.

FIG. 14 is a schematic plan view of a directional coupler type lightswitch manufactured by the method of the present invention. Thesectional construction of the light amplifier section A₁ (A₂) of thislight switch is the same as that of the total reflection type lightswitch shown in FIG. 12.

The sectional construction of the coupling section (switching section)has a first upper cladding layer 19'a, an etch stop layer 25, a secondupper cladding layer 19'b, and a surface layer 20' formed of p-doped InPsemiconductor, p-doped InGaAsP semiconductor, p-doped InP semiconductor,and p-doped InGaAs semiconductor, respectively, as shown in FIG. 15,which is a sectional view taken along the line XV--XV of FIG. 14, beingthe same as that shown in FIG. 13 except that Zn diffusion area 24 isnot formed.

The waveguide except the coupling section S has the same sectionalconstruction as the above-mentioned coupling section S except that anupper electrode is not mounted and the entire surface is covered withthe insulating film 21.

FIG. 16 is a schematic plan view showing an example of semiconductoroptical component in which a 1×2 optical coupler and a light amplifiersection are integrated. The light amplifier section A₁ (A₂) of thisoptical component has a sectional construction as shown in FIG. 12. Thesectional construction of the waveguide is such that the entire surfaceof the second cladding layer 19'b and the etch stop layer 25 is onlycovered with an insulating film 21 as shown in FIG. 17, which is asectional view taken along the line XVII--XVII of FIG. 16.

For this optical component, light which is introduced through a port 26is divided into two components at the branch section, and each of lightis transmitted through respective branching waveguides 27 and 28. Withthis optical component, the degree of amplification at the lightamplifier section A₁ (A₂) can be changed by changing the value ofcurrent injected through the light amplifier section A₁ (A₂). Therefore,the output of light going out of the respective ports 27a and 28a of thebranching waveguide 27 and the branching waveguide 28 can be changed, bywhich any branching ratio can be obtained.

EXAMPLES Example 1

A total reflection type light switch shown in FIGS. 1 through 6 wasmanufactured as described below.

First, a 0.20 μm-thick waveguide layer (absorption edge wavelength:λ_(g) =1.15 μm) 12 formed of n-type InGaAsP, a 0.20 μm-thick activelayer (λ_(g) =1.30 μm) 13 formed of undoped InGaAsAsP, a 0.20 μm-thickwaveguide layer (λ_(g) =1.15 μm) 14 formed of p-doped InGaAsP, a 1.40μm-thick cladding layer 15 formed of p-doped InP, and a 0.20 μm-thicksurface layer 16 formed of p-doped InGaAsP were successively laminatedon the entire surface of a substrate 11 formed of n-type InP by theMOCVD method to produce a laminated body with a total thickness of 2.20μm (FIG. 2).

Then, a SiO₂ film 17 was formed on the surface layer 16. With this filmbeing used as a mask, the entire portion of the laminated body excludingthe area a₁ (a₂) of 500 μm in length and 100 μm in width was etched andremoved to expose the surface 11a of the substrate 11 (FIG. 3).

Again with the SiO₂ film 17 being used as a mask, a 1.00 μm-thickwaveguide layer (λ_(g) =1.02 μm) 18 formed of undoped InGaAsP, a 0.90μm-thick cladding layer 19 formed of undoped InP, and a 0.20 μm-thicksurface layer 20 formed of undoped InGaAs were successively laminated onthe exposed surface 11a of the substrate 11 with the MOCVD method toproduce a laminated body b with a total thickness of 2.10 μm (FIG. 4).

Then, the SiO₂ film was removed, and elevated steps or ridges wereformed by applying photolithography to the entire surface; the ridge hada path width of 2.0 μm at the light amplifier section A₁ (A₂) and 8.0 μmat the waveguides 2, 3, 5, and 6. Thereafter, the entire surface wascovered with a SiO₂ film again (FIG. 1).

Finally, AuGeNi/Au was deposited on the back surface of the substrate tomount a common lower electrode 22. The SiO₂ film 21 on the lightamplifier section A₁ (A₂) and the switching section S was removed. Forthe switching section S, a Zn diffusion zone 24 was formed by diffusingZn from the portion where the SiO₂ film was removed. In this zone,Ti/Pt/Au was deposited to mount upper electrodes 23, 23, and 4 (FIGS. 5and 6).

For this light switch, when the value of current injected to the lightamplifier A₂ was 200 mA, the insertion loss was 0 dB, and the extinctionratio was 27 dB in the switch state I. When the value of currentinjected to the light amplifier A₁ was 230 mA in the switch state II,the insertion loss was 0 dB and the extinction ratio was 36 dB.

Example 2

A total reflection type light switch having a light amplifier sectionand a switching section of sectional construction as shown in FIGS. 12and 13 and a planar pattern as shown in FIG. 1 was manufactured asdescribed below.

First, as shown in FIG. 2, a 0.23 μm-thick waveguide layer (λ_(g) =1.05μm) 12 formed of n-type InGaAsP, a 0.14 μm-thick active layer (λ_(g)=1.30 μm) 13 formed of undoped InGaAsAsP, a 0.23 μm-thick waveguidelayer (λ_(g) =1.05 μm) 14 formed of p-doped InGaAsP, a 2.00 μm-thickcladding layer 15 formed of p-doped InP, and a 0.20 μm-thick surfacelayer 16 formed of p-doped InGaAs were successively laminated on theentire surface of a substrate 11 formed of n-type InP by the MOCVDmethod to produce a laminated body with a total thickness of 2.80 μm.

Then, a SiO₂ film 17 was formed on the surface layer 16. With this filmbeing used as a mask, the entire portion of the laminated body excludingthe area a₁ (a₂) of 500 μm in length and 50 μm in width was etched andremoved to expose the surface 11a of the surface 11 (FIG. 3).

Again with the SiO₂ film 17 being used as a mask, a 0.60 μm-thickwaveguide layer (λ_(g) =1.15 μm) 18' formed of undoped InGaAsP, a 0.50μm-thick first upper cladding layer 19'a formed of undoped InP, a 0.01μm-thick etch stop layer 25 formed of undoped InGaAsP, a 1.50 μm-thicksecond upper cladding layer 19'b formed of undoped InP, and a 0.20μm-thick surface layer 20' formed of undoped InGaAs were successivelylaminated on the exposed surface 11a of the substrate 11 with the MOCVDmethod as shown in FIG. 7 to produce a laminated body b' with a totalthickness of 2.81 μm (FIG. 7).

Then, the SiO₂ film 17 was removed, and a pattern of SiO₂ film 17' wasformed on the surface layer 16 and the surface layer 20' as shown inFIG. 1 such that the path width of the light amplifier section A₁ (A₂)was 2.0 μm, and that of the waveguide 2, 3, 5, and 6 was 8.0 μm.Thereafter, the entire surface was etched with an etchant includingsulfuric acid to remove the exposed surface layer. Thus, in the lightamplifier section A₁ (A₂), a sectional construction as shown in FIG. 8was formed, whereas in the waveguides 2, 3, 5, and 6 and the switchingsection S, a sectional construction as shown in FIG. 9 was formed (FIGS.8 and 9).

Then, etching was performed using an etchant including hydrochloric acidin place of an etchant including sulfuric acid so that a part of theupper cladding layer 15 was removed at the light amplifier section A₁(A₂) and the second upper cladding layer 19'b was removed at thewaveguides 2, 3, 5, and 6 and the switching section S. As a result, aplanar pattern was formed such that respective sectional constructionswere as shown in FIGS. 10 and 11.

Thus, the light amplifier section A₁ (A₂) with a path width of 2.0 μmand the waveguides 2, 3, 5, and 6 with a path width of 8.0 μm wereformed. The ridge height (h₁) of the light amplifier section A₁ (A₂) was2.20 μm, whereas the ridge height (h₂) of the waveguide 2, 3, 5, and 6was 1.70 μm; the ridge height of the light amplifier section beinggreater than that of the waveguide.

Then, after all the SiO₂ film 17' was removed temporarily, a SiO₂ film21 was formed to cover the entire surface. Thereafter, AuGeNi/Au wasdeposited on the back surface of the substrate to mount a common lowerelectrode 22. The insulating film 21 on the light amplifier section A₁(A₂) and the switching section S was removed. For the switching sectionS, a Zn diffusion zone 24 was formed by diffusing Zn from the portionwhere the insulating film was removed. In this zone, Ti/Pt/Au wasdeposited to mount upper electrodes 23, 23, and 4, respectively. Thus,the light amplifier section A₁ (A₂) and the switching section S wereformed as shown in FIGS. 12 and 13.

For this light switch, when the value of current injected to the lightamplifier A₂ was 180 mA in the switch state I, the insertion loss was 0dB, and the extinction ratio was 28 dB. When the value of currentinjected to the light amplifier A₁ was 200 mA in the switch state II,the insertion loss was 0 dB and the extinction ratio was 36 dB.

Further, a light switch with the same sectional construction and adifferent path width was manufactured by keeping the path width of thewaveguide 8.0 μm and only changing the path width pattern of the lightamplifier section A₁ (A₂) when a mask pattern was formed by the SiO₂film 17. With the injected current to one of the light amplifier sectionA₁ (A₂) being set at 250 mA, the amplification factor was measured. Theresult is shown in FIG. 18 as a relationship between the path width ofthe light amplifier section A₁ (A₂) and the amplification factor. Asseen from FIG. 18, the amplification factor is at a maximum when thepath width is 2.0 μm. In addition, it is difficult to form the lightamplifier section because its path width is too narrow. Therefore, thepath width of the light amplifier section is preferably about 2.0 μm.

Example 3

A directional coupler type light switch as shown in FIG. 14 wasmanufactured as described below.

As shown in FIG. 2, a 0.23 μm-thick waveguide layer (λ_(g) =1.05 μm) 12formed of n-type InGaAsP, a 0.14 μm-thick active layer (λ_(g) =1.30 μm)13 formed of undoped InGaAsAsP, a 0.23 μm-thick waveguide layer (λ_(g)=1.05 μm) 14 formed of p-doped InGaAsP, a 2.00 μm-thick cladding layer15 formed of p-doped InP, and a 0.20 μm-thick surface layer 16 formed ofp-doped InGaAs were successively laminated on the entire surface of asubstrate 11 formed of n-type InP by the MOCVD method to produce alaminated body with a total thickness of 2.80 μm.

Then, a SiO₂ film 17 was formed on the surface layer 16. With this filmbeing used as a mask, the entire portion of the laminated body excludingthe area a₁ (a₂) of 500 μm in length and 50 μm in width was etched andremoved to expose the surface 11a of the surface 11 (FIG. 3).

Again with the SiO₂ film 17 being used as a mask, a 0.60 μm-thickwaveguide layer (λ_(g) =1.15 μm) 18' formed of undoped InGaAsP, a 0.50μm-thick first upper cladding layer 19'a formed of p-doped InP, a 0.01μm-thick etch stop layer 25 formed of p-doped InGaAsP, a 1.50 μm-thicksecond upper cladding layer 19'b formed of p-doped InP, and a 0.20μm-thick surface layer 20' formed of p-doped InGaAs were successivelylaminated on the exposed surface 11a of the substrate 11 with the MOCVDmethod as shown in FIG. 7 to produce a laminated body with a totalthickness of 2.81 μm.

Then, the SiO₂ film 17 was removed, and a pattern of SiO₂ film 17' wasformed on the surface layer 16 and the surface layer 20' as shown inFIG. 14 such that the path width of the light amplifier section A₁ (A₂)was 2.0 μm, and that of the directional coupler section and otherwaveguide was 8.0 μm. Thereafter, the entire surface was etched with anetchant including sulfuric acid to remove the exposed surface layer.Subsequently, etching was performed using an etchant includinghydrochloric acid in place of an etchant including sulfuric acid so thata part of the upper cladding layer 15 was removed at the light amplifiersection A₁ (A₂) and the second upper cladding layer 19'b was removed atthe waveguides and the directional coupler section. As a result, aplanar pattern was formed such that respective sectional constructionswere as shown in FIGS. 10 and 11.

Thus, the light amplifier section A₁ (A₂) with a path width of 2.0 μmand the waveguides with a path width of 8.0 μm were formed. The ridgeheight (h₁) of the light amplifier section A₁ (A₂) was 2.20 μm, whereasthe ridge height (h₂) of the waveguide 2, 3, 5, and 6 was 1.70 μm; theridge height of the light amplifier section being greater than that ofthe waveguide.

Then, after all the SiO₂ film 17' was removed temporarily, a SiO₂ film21 was formed again to cover the entire surface. Thereafter, AuGeNi/Auwas deposited on the back surface of the substrate to mount a commonlower electrode 22. The insulating film 21 on the light amplifiersection A₁ (A₂) and the switching section S were removed, where Ti/Pt/Auwas deposited to mount upper electrodes 23, 23, and 4. Thus, the lightamplifier section A₁ (A₂) and the directional coupler S of a sectionalconstruction as shown in FIGS. 12 and 15, respectively, were formed.

For this light switch, the injected current for amplifying the lightpassing through the port was 230 mA and 240 mA when the directionalcoupler S is in a bar state and in a cross state, respectively. Theinsertion loss in each case was 2.20 dB and 1.80 dB, respectively.

Example 4

A 1×2 optional coupler shown in FIG. 16 was manufactured as describedbelow.

As shown in FIG. 2, a 0.23 μm-thick waveguide layer (λ_(g) =1.05 μm) 12formed of n-type InGaAsP, a 0.14 μm-thick active layer (λ_(g) =1.30 μm)13 formed of undoped InGaAsAsP, a 0.23 μm-thick waveguide layer (λ_(g)=1.05 μm) 14 formed of p-doped InGaAsP, a 2.00 μm-thick cladding layer15 formed of p-doped InP, and a 0.20 μm-thick surface layer 16 formed ofp-doped InGaAs were successively laminated on the entire surface of asubstrate 11 formed of n-type InP by the MOCVD method to produce alaminated body with a total thickness of 2.80 μm.

Then, a SiO₂ film 17 was formed on the surface layer 16. With this filmbeing used as a mask, the entire portion of the laminated body excludingthe area a₁ (a₂) of 500 μm in length and 50 μm in width was etched andremoved to expose the surface 11a of the surface 11 (FIG. 3).

Again with the SiO₂ film 17 being used as a mask, a 0.60 μm-thickwaveguide layer (λ_(g) =1.15 μm) 18' formed of undoped InGaAsP, a 0.50μm-thick first upper cladding layer 19'a formed of undoped InP, a 0.01μm-thick etch stop layer 25 formed of undoped InGaAsP, and a 1.70μm-thick second upper cladding layer 19'b formed of undoped InP weresuccessively laminated on the exposed surface 11a of the substrate 11with the MOCVD method as shown in FIG. 7 to produce a laminated bodywith a total thickness of 2.81 μm.

Then, the SiO₂ film 17 was removed, and a pattern of SiO₂ film 17' wasformed on the surface layer 16 and the second upper cladding layer 19'bas shown in FIG. 16 such that the path width of the light amplifiersection A₁ (A₂) was 2.0 μm, and that of the waveguide was 8.0 μm.Thereafter, the entire surface was etched with an etchant includingsulfuric acid to remove the exposed surface layer at the light amplifiersection A₁ (A₂) and the waveguides. Subsequently, etching was performedusing an etchant including hydrochloric acid in place of an etchantincluding sulfuric acid so that a part of the upper cladding layer 15was removed at the light amplifier section A₁ (A₂) and the second uppercladding layer 19'b was removed at the waveguides. As a result, a planarpattern was formed such that respective sectional constructions were asshown in FIGS. 10 and 11.

Thus, the light amplifier section A₁ (A₂) with a path width of 2.0 μmand the waveguides with a path width of 8.0 μm were formed. The ridgeheight (h₁) of the light amplifier section A₁ (A₂) was 2.20 μm, whereasthe ridge height (h₂) of the waveguide was 1.70 μm; the ridge height ofthe light amplifier section is greater than that of the waveguide.

Then, after all the SiO₂ film 17' was removed temporarily, a SiO₂ film21 was formed again to cover the entire surface. Thereafter, AuGeNi/Auwas deposited on the back surface of the substrate to mount a commonlower electrode 22. The insulating film 21 on the light amplifiersection A₁ (A₂) was removed, where Ti/Pt/Au was deposited to mount upperelectrodes 23, 23, respectively. Thus, the light amplifier section A₁(A₂) and the waveguides were formed as shown in FIGS. 12 and 17.

For this 1×2 optical coupler, when the injected current to the lightamplifier section A₁ (A₂) was set at 240 mA, a branching ratio of 15 dBwas obtained.

AVAILABILITY IN INDUSTRY

For a semiconductor optical component manufactured by the method of thepresent invention, an insertion loss at the light amplifier section canbe reduced to 0 dB, and the extinction ratio can be enhanced when thecomponent operates as a switch.

These are the effects obtained by the fact that the ridge-shaped lightamplifier section on the substrate is formed so that its path width isnarrower than that of the ridge-shaped waveguide. Since the path widthof the light amplifier section is narrower than that of the waveguide,the confining state of the injected current is enhanced sufficiently, sothat the current density therein is increased. As a result, light can beamplified highly efficiently.

Also, the ridge height of the light amplifier section greater than thatof the waveguide can further increases the coupling efficiency of light.

We claim:
 1. A semiconductor optical component comprising:elevatedstepped semiconductor light amplifier sections formed on a substrate,each said semiconductor light amplifier section having a path width, andelevated stepped semiconductor waveguides connected thereto to saidsemiconductor light amplifier sections and formed on said substrate,each said semiconductor waveguide having a path width, wherein the pathwidth of each said elevated stepped semiconductor light amplifiersection is narrower than the path width of each respective said elevatedstepped semiconductor waveguide.
 2. A semiconductor optical componentaccording to claim 1 wherein each said elevated stepped semiconductorlight amplifier section has a stepped height and each said elevatedstepped semiconductor waveguide has a stepped height, and the steppedheight of each said ridge-shaped semiconductor light amplifier sectionis greater than the stepped height of each respective said ridge-shapedsemiconductor waveguide.
 3. A semiconductor optical component accordingto claim 1 wherein said semiconductor optical component is a totalreflection light switch.
 4. A semiconductor optical component accordingto claim 1 wherein said semiconductor optical component is a directionalcoupler light switch.
 5. A semiconductor optical component according toclaim 1 wherein said semiconductor optical component is a one input/twooutput optical coupler.
 6. A manufacturing method for a semiconductoroptical component in which elevated stepped semiconductor lightamplifier sections and elevated stepped semiconductor waveguidesconnected thereto are integrated on the same substrate, each of saidsemiconductor light amplifier sections and said semiconductor waveguideshaving a path width, comprising the steps of:forming said elevatedstepped semiconductor light amplifier sections with said path widththereof narrower than the path width of said elevated steppedsemiconductor waveguides at appropriate positions on said substrate; andforming said elevated stepped semiconductor waveguides at positions onsaid substrate other than said appropriate positions with saidsemiconductor waveguides being connected to said semiconductor lightamplifier sections.
 7. A manufacturing method for a semiconductoroptical component according to claim 6 wherein each said elevatedstepped semiconductor light amplifier section has a stepped height andeach said elevated stepped semiconductor waveguide has a stepped height,and further comprising the step of forming each said elevated steppedsemiconductor light amplifier section in such a manner that the steppedheight thereof is greater than the stepped height of said elevatedstepped semiconductor waveguide.